1. Field of the Invention
The present invention relates to a method of realizing highly accurate feature detection even when variation occurs, for example, in a size or direction of a detection target pattern.
2. Description of the Related Art
In the field of pattern recognition, there has been a strong demand for a method capable of realizing accurate feature detection regardless of variation in a size or a direction of a recognition target. There has also been a strong demand to know what type of variation a pattern has received.
For example, a method has been discussed for efficiently detecting a face image even in a non-frontal view (Japanese Patent Application Laid-Open No. 2004-133637). According to this method, a correlation is obtained between an input image and a template image of a predetermined size. The template image represents an average face image. When it is determined that the input image is not a frontal view, the template image is rotated by a predetermined angle or angles which are sequentially updated, and collation is repeated.
A method has also been described for preparing affine transformation parameters each corresponding to variation of a human face image which is a recognition target, detecting the face image after inverse transformation, and combining a plurality of detection results (Japanese Patent Application Laid-Open No. 2000-90191). In this case, the variation corresponds to positional shifting of the face image, inclination, a change in vertical direction, or a change in horizontal direction. As a combining method, a highest point or decision by majority is employed.
However, according to the aforementioned conventional transformation based method, many templates or parameters need to be prepared for pattern variation and, to obtain a highly accurate estimation about variation, a large amount of processing is needed. As the method for combining many detection results, the highest point or the decision by majority is not sufficient to estimate features regarding variation with a high degree of accuracy.